Blockers are unwanted signals that can interfere with and adversely affect the performance of communication receivers. Blocker can be in-band or out-of-band blockers and may disturb the receiver in different ways. For example, an in-band blocker can desensitize the receiver due to reciprocal or spurious mixing, or through inter-modulation. Whereas a large out-of-band blocker can saturate the receiver front-end, and hence reduces the receiver gain, which may result in elevation of the noise contribution of the subsequent baseband blocks.
In today's densely congested wireless spectrum, design of blocker-tolerant receivers is crucial in achieving a decent performance. Existing solution may utilize multitude of off-chip filters such as surface acoustic wave (SAW) and/or bulk acoustic wave (BAW) filters that are costly and may have large form-factors. On the other hand, co-existence of difference wireless protocols is an important issue in modern hand-held communication devices such as mobiles phones. Many hand-held communication devices use both wireless local area network 2G (WLAN2G) and Bluetooth transceivers, the industrial, scientific and medical (ISM) band for which is quite close to the long-term evolution (LTE) band. For example, the co-existence of the unwanted LTE signals can degrade the performance of WLAN2G. The out-of-band (OOB) noise of the WLAN2G transmitter can leak into the input of the LTE receiver, and has to be significantly less than a noise floor of the LTE receiver. Typically, the antenna for WLAN2G and cellular band is shared.
Currently, in order to reduce the OOB noise of the WLAN2G in the LTE band to a negligible level, an inter-stage SAW filter is added between the power amplifier (PA) and the PA driver (PAD). An existing large body of research for mitigation of receiver (RX) band noise in frequency-division duplexing (FDD) systems is mostly focused on baseband (BB). For example, low noise BB designs and more filtering (e.g., active and/or passive) in BB domain to reduce the digital-to-analog converter (DAC) and BB noise has been the focus of some of these research projects. The low noise BB designs may be most problematic as the noise at the BB includes noise contribution from most amplification stages. Use of passive-mixers instead of active-mixers has also been considered to reduce the noise and non-linearity contributions from the active-mixers.